The present invention relates to a toner used in a recording method using electrophotography, electrostatic recording, electrostatic printing, toner-jet recording, and the like.
As electrophotography, a number of methods have been known such as those disclosed in U.S. Pat. No. 2,297,691, and Japanese Patent Publication Nos. 42-23910, and 43-24748. In general, an electrostatically charged image is formed on a photosensitive member by various means, the electrostatically charged image is then developed using a toner, the toner image is transferred on a transferring material such as paper, and is fixed by applying heat and/or pressure, or exposing to solvent vapor to form a toner image.
Although various methods and equipment have been developed for the final step described above, i.e. the fixation of toner images onto a sheet such as paper, a method most generally used today is the hot-pressing method using a stationary heater through hot rollers or heating films.
In the hot-pressing method using hot rollers, a sheet carrying toner images is passed between the hot rollers having surfaces to which the toner is not adhered while allowing the surface of the rollers to contact with the toner image surface of the sheet under a pressure. By this method, since the surface of the hot rollers contacts with the toner images on the sheet under a pressure, the thermal efficiency in the fusion of the toner onto the sheet is very high, and the images can be fixed promptly.
In the hot-rolling method, however, since the surfaces of the heating rollers contact with softened or molten toner images under a pressure, a part of the toner images is adhered and transferred onto the surfaces of the fixing rollers, and then transferred to the sheet again, often causing the contamination of the sheet, known as the offset phenomenon. This offset phenomenon is significantly affected by the speed and temperature for fixation. In general, when the fixation speed is low, the surface temperature of the heating rollers is set relatively low; and when the fixation speed is high, the surface temperature of the heating rollers is set relatively high. This is done such that the amount of heat provided from the hot rollers to the toner is made substantially constant regardless of the fixing speed.
The toner on the sheet forms a number of toner layers. If the fixing speed is high, and the surface temperature of the hot rollers is high, the temperature difference between the toner layer contacting with the hot rollers and the lowermost toner layer contacting with the sheet is large. If the surface temperature of the hot rollers is high, the uppermost toner layer is excessively softened or melted to cause the offset phenomenon easily. If the surface temperature of the hot rollers is low, the lowermost toner layer is not melted sufficiently for fixation, often causing a phenomenon in which the toner not to fix on the sheet, known as cold offset.
In order to solve such problems, when the fixing speed is high, a method for anchoring the toner into the sheet by elevating the pressure for fixation is generally used. In this method, the roller temperature can be lowered to some extent, and the hot offset phenomenon of the toner can be prevented. However, since the shearing force applied to the toner becomes very large, the sheet is wound around the fixing roller to cause winding offset, or when a separating blade is used for separating the sheet from the fixing rollers, the trace of the separating blade often appears on the fixed images. Furthermore, because of a high pressure, line images are often defaced during fixing, or the toner is often scattered, causing the degradation of fixed images.
The toner for forming electrostatic images must have positive or negative charge depending on the polarity of the electrostatic images to be developed and the method of developing,
To make the toner charged, the frictional chargeability of the resin that is a component of the toner can be used, but the chargeability of the resin is generally low. Therefore, to impart desired frictional chargeability to the resin, a dye and/or a pigment for imparting chargeability, or further a charge-controlling agent is added to the toner.
The known charge-controlling agents for positive frictional chargeability include nigrosine dyes, azine dyes, copper phthalocyanine pigments, quaternary ammonium salts, or polymers having quaternary ammonium salts on the side chains. The known charge-controlling agents for negative frictional chargeability include the metal complex salts of monoazo dyes; the metal complexes or metal salts of salicylic acid, naphthoic acid, dicarboxylic acids, or the derivatives thereof; or resins having acid groups.
Among these, colorless, white, or light color agents are useful as the charge-controlling agent for color toners.
Heretofore, toners containing a metal compound of an oxycarboxylic acid have been proposed. For example, toners containing aluminum compound of aromatic oxycarboxylic acid as charge promoting additives are disclosed in Japanese Patent Application Laid-Open No. 6-214424; toners containing the boron compound of benzilic acid are disclosed in Japanese Patent Application Laid-Open Nos. 62-63941, 2-221967, 3-39973, and 5-72812; a color toner containing a boron complex salt of benzilic acid and silicone-oil-treated hydrophobic inorganic fine powder is disclosed in Japanese Patent Application Laid-Open No. 5-165257; and a toner containing a metal complex salt of benzilic acid having an amide as the counter ion is disclosed in Japanese Patent Application Laid-Open No. 6-301240. However, although these toners have somewhat improved charge speed, they have a disadvantage in that the frictional charging of the toner is insufficient. To solve the above-described problems, Japanese Patent Application Laid-Open No. 10-312089 discloses a toner using the combination of a boron complex salt of benzilic acid and a metal salt of a derivative of salicylic acid. According to examinations by the inventors of the present invention, although the combination use of a boron complex salt of benzilic acid and a metal salt of a derivative of salicylic acid improves the frictional charging of the toner and the charge speed of the toner, the distribution of the toner""s frictional charging becomes broad due to the mixed presence of charge-controlling agents having different electrification series, and improvement is still required.
Also, there are problems related to the dispersion of various additives used in the manufacture of the toner. In particular, wax is difficult to disperse uniformly, and if dispersion is not uniform, there are problems not only in the fixation properties of the toner, but also in developing properties. These problems are even more significant due to the recent particle-size reduction.
The present invention provides a toner without the above-described problems.
Therefore, it is an object of the present invention to provide a toner that has good fixing properties at low temperatures in both medium- to high-speed machines using hot fixing rollers, and medium- to low-speed machines of the hot-pressing fixation method using stationary heaters through heat-resistant films, without the contamination of heating members due to offset from a low temperature to a high temperature.
It is another object of the present invention to provide a toner that excels in good fixing properties at low temperatures and exhibits good half-tone fixing properties while its particle diameter is reduced and its high colorant (particularly magnetic material) content is increased.
It is a further object of the present invention to provide a toner that excels in frictional charging and charge speed, maintains good environmental stability, and can form high-quality images for a long period of time.
According to an aspect of the present invention, there is provided a toner containing at least a binder resin, a colorant, a wax, and an organic aluminum compound, wherein,
i) the binder resin has an acid value of 1 to 40 mgKOH/g,
ii) the binder resin contains 2 to 50 percent by weight of tetrahydrofuran (THF)-insoluble matter based on the weight of the binder resin,
iii) the tetrahydrofuran-soluble matter of said binder resin has a main peak in the molecular weight range of from 2,000 to 30,000 in a chromatogram by gel permeation chromatography (GPC), and
iv) the organic aluminum compound is an aluminum compound of substituted or unsubstituted benzilic acid represented by the following Formula (1): 
xe2x80x83wherein R1 and R2 may be the same or different and each represents a substituent selected from the group consisting of straight-chain or branched alkyl, alkenyl, alkoxy, halogen, nitro, cyano, amino, carboxy, and hydroxy; and m and n each are an integer of from 0 to 5.
According to another aspect of the present invention, there is provided an image forming method, comprising at least
(a) a charging step for charging an image carrier that carries electrostatic images (or an image bearing member);
(b) an exposing step for forming electrostatic images by exposure of the charged image carrier;
(c) a developing step for developing the electrostatic images with a toner carried on the surface of a toner carrier (or a toner carrying member) to form toner images;
(d) a transferring step for transferring the toner images formed on the surface of the image carrier onto a transfer material via or not via an intermediate transfer member; and
(e) a fixing step for fixing the transferred toner images to the transfer material; wherein the toner contains at least a binder resin, a colorant, a wax, and an organic aluminum compound,
i) the binder resin has an acid value of 1 to 40 mgKOH/g,
ii) the binder resin contains 2 to 50 percent by weight of tetrahydrofuran (THF)-insoluble matter based on the weight of the binder resin,
iii) the tetrahydrofuran-soluble matter of the binder resin has a main peak in the molecular weight range of from 2,000 to 30,000 in a chromatogram by gel permeation chromatography (GPC), and
iv) the organic aluminum compound is an aluminum compound of substituted or unsubstituted benzlic acid represented by the above Formula (1). 